This invention relates generally to devices for cooling, generating power, compressing, pumping, and evacuating to pressure below ambient.
There are numerous references in the literature to miniaturized devices whose recent appearance is coincident with the application of microfabrication processes to the production of mechanical systems. Microfabrication processes are those typically associated with integrated circuit production, but more generally include processes capable of producing components and assemblies with micron-sized features and producing a plurality of assemblies or components simultaneously or in xe2x80x9cbatchesxe2x80x9d. The fine dimensional tolerances of microfabrication processes means that entire classes of novel miniaturized machines can be realized. The ability to produce multiple parts simultaneously means that in many cases these novel machines may be produced efficiently and in great numbers; batching leads to economy-of-scale reduction in the production costs.
The realization that many macroscopic machines can be fully miniaturized has led to a class of devices; for examples see xe2x80x9cSilicon Micromachiningxe2x80x9d, Cambridge University Press, 1998 and xe2x80x9cHandbook of Microlithography, Micromachining, and Microfabricationxe2x80x9d, SPIE Press, 1997, incorporated herein by reference to the extent not inconsistent herewith.
One way to enhance microelectronic system efficiency as well as increase reliability is to cool electronic devices to temperatures that substantially reduce power consumption/generation. This however, implies a substantial cooling system. The large heat density produced by present generation electronics is one of the main problems facing present cooling systems. Present heat densities are now exceeding 30 W/cm2. However, if these same circuits could be cooled to cryogenic temperatures, they could operate at higher frequencies, with reduced power, more reliably, and at lower voltages as indicated in the references by E. Simoen and P. Ghazavi (citations below).
Three of the most important considerations facing any novel active cooling technology are cost of implementation, reliability, and efficiency. If the cooling device is prohibitively expensive and/or unreliable or if the cooling device uses substantially more power than is saved, many of the benefits derived from cooling vanish. Efficiency is especially important when cryogenic cooling is considered, since most common cryogenic systems operate at only a few percent of Carnot efficiency.
Present cooling and refrigeration technologies are unable to satisfy present demands. For example, as CMOS electronics have approached the 0.18 xcexcm gate size, they have begun to generate heat densities that require active cooling if these electronic devices are to operate efficiently and reliably. To date there have been many proposed solutions to the problem of cooling very dense microelectronics, but very few of these proposals provide substantial sub-ambient cooling power, and none do so efficiently.
There are also many applications for cryogenic cooling, which extend beyond the needs of conventional electronics, such as superconducting electronics and infrared imaging sensors cooled to temperatures of 35 K and below. There are many applications for which superconducting electronics, operating at both high (70-35 K) and low (35-4 K) temperatures, provide the only feasible solution. Likewise there are many high-precision long-wavelength remote sensing applications, which can only be realized if the sensing detector is maintained at very low temperatures. Often, however these applications have limited space available for the cryogenic system and limited power with which to drive such a system. These two requirements greatly increase the cost and difficulty of realizing present cryogenic support systems.
Present cryogenic cooling technologies suffer from one or more of the following limitations: limited lifetime, high cost, large size, excessive weight, vibration, and ineffective integration with the objects to be cooled. Commercial and tactical cryocoolers that operate at liquid nitrogen temperatures cost on the order of tens of thousands of dollars, generally have lifetimes of less than two years, have limited heat lift, and do not incorporate effective vibration control. Low-temperature cryocoolers, such as Gifford-McMahon cryocoolers, weigh several hundred pounds, have high vibration, and require several kilowatts of power input for a few watts of heat lift at 10 K and below. Aerospace cryocoolers that have long lifetimes and vibration control can cost over one million dollars each. These cryocoolers have high efficiency for temperatures above 50 K; however, as their operating temperature decreases, their efficiency gets much worse, and their practical minimum temperature is about 30 K. Further, all present cryocoolers require complex and expensive assembly procedures that do not readily lend themselves to mass production; therefore, they are limited in their capacity to enjoy economy of scale cost reductions.
For all of these reasons, there has been a need in developing miniaturized and highly efficient cryogenic systems using Micro-Electro-Mechanical Systems (MEMS) technologies. For example, see U.S. Pat. Nos. 5,932,940, 5,941,079, and 5,457,956. Unfortunately, applying the common principles of refrigeration and cryogenic design to systems with dimensional scales of microns and millimeters has posed substantial problems. For example, U.S. Pat. No. 5,932,940 proposes a reverse Brayton cycle refrigerator, but to extract useful amounts of heat the proposed system must operate at very large rotational speeds, 300-1000 krpms. Among the many technical challenges presented in reducing such a design to practice is the fact that this turbine speed requires complex load bearing assemblies; refer to K. S. Breuer et al. xe2x80x9cChallenges for High-Speed Lubrication in MEMSxe2x80x9d. To operate properly, these bearings must be fabricated with such precision that present MEMS process technologies are not capable of satisfying the requirements.
U.S. Pat. Nos. 5,457,956 and 5,941,079 appear to require a material that has thermal properties outside those of known materials. In addition, the frequency at which these proposed MEMS compressors must operate to produce a useful cooling effect is too high for an efficient resonant system.
Chemical charge storage batteries have provided the majority of the portable energy sources for powering portable electronics. Such batteries, however, are limited in both power density and lifetime, particularly when it is desired that the power source be reusable. For these reasons and since the power demands of portable electronic devices have been steadily increasing, chemical batteries have become increasingly inadequate. By comparison to batteries, heat engines, such as internal combustion engines, generate large amounts of power, but are typically massive, making them incompatible with portable applications. One of the reasons that heat engines produce large amounts of power results from the large energy density of liquid fuels, much larger per unit mass than any known charge storage device. Thus, if liquid fuels or pressurized gases can be used to drive a miniaturized electrical power generator, the result would be a revolution in portable energy technology which would enjoy increased operating times at higher levels of power consumption, reduced operating expense, higher levels of reusability, and a more environmentally benign operational effect.
Of the proposed solutions to portable power generation, two examples are found in U.S. Pat. Nos. 5,932,940 and 6,109,222. U.S. Pat. No. 5,932,940 proposes a microscale gas turbine operating at very large rotational speeds, which can collect the energy released during the gas-phase combustion of a fuel and oxidizer, and convert it into electrical energy. The miniaturization of the gas turbine provides many technical advantages. However, the very large rotational speed required to produce useful effects has presented severe difficulties in producing an operating device, chief among them the fabrication of high precision gas-bearings. The tolerance requirements of these bearings have made implementation very difficult and will quite dramatically increase production costs; refer to K. S. Breuer et al. xe2x80x9cChallenges for High-Speed Lubrication in MEMSxe2x80x9d.
On the other hand, U.S. Pat. No. 6,109,222 proposes a micro/meso-scale reciprocating piston that oscillates between combustion cylinders. In this case, the energy released during combustion of the gas-phase products is collected either mechanically from gas jets or via magnetic commutation. Again, it is not clear an operating device can be prepared with the needed efficiency or reliability. In fact all other presently proposed miniaturized power-generation technologies seem to have practical limitations to their usefulness including limited energy generation capabilities, questionable reliability, severe operational inefficiencies, complicated and expensive manufacture, and the requirement for tolerances which presently exceed capabilities of microfabrication processes.
There are numerous potential applications for miniaturized pumps for moving fluid volumes and compressors for increasing gas pressures. Such pumps (or compressors for gases) can be used to control scaled-down chemical processes, to meter fluids, circulate compressed fluids for temperature control processes, dispense medicines, and actuate miniaturized hydraulic systems. Many MEMS pumps have been proposed; representative examples can be found in U.S. Pat. Nos. 5,932,940, 6,109,889, 5,336,062, 6,106,245, 6,019,882, and 5,788,468. All of these inventions have limitations; U.S. Pat. No. 5,932,940 has the same limitations detailed previously. U.S. Pat. Nos. 6,109,889 and 5,336,062 are suited to very small applications when neither a large pressure head nor a significant volume is required; these two pumps are involved almost exclusively with micrometering applications and are not suited for more robust general purpose pumping applications. U.S. Pat. No. 6,106,245 discloses a diaphragm pump, with an electrostatically actuated polymer diaphragm. To move significant amounts of fluids at useful pressures, a number of these pumps would have to be ganged in a series-parallel configuration. Further, the continuously flexing diaphragm introduces a serious reliability issue, especially considering that the diaphragm is fashioned from a polymer and in some configurations is bi-stable exhibiting a xe2x80x9csnappingxe2x80x9d behavior. U.S. Pat. No. 6,019,882 discloses an electro-osmotic pump. The electro-osmotic process is observed when an electrolyte, a liquid containing solvated ions, comes into contact with a solid under the influence of an electric field. Because an electrolyte forms a charged layer at the interface between the solid and the liquid, an electric field can produce a net drift of the charged species, resulting in fluid flow at increased pressure. As disclosed in U.S. Pat. No. 6,019,882, the electro-osmotic effect is significant for porous media and in this case, the system can generate very large hydraulic pressures. The drawback to this invention is the fact that this effect is only observed for special fluids containing ionic species; thus to pump any fluid in which ionic species are not present requires a complex secondary pumping system. In fact pumping vaporized fluids, as proposed in U.S. Pat. No. 6,019,882, will almost certainly involve the fabrication of a diaphragm-based pump, with some of the same reliability limitations affecting U.S. Pat. No. 6,106,245. The diaphragm-based design will be required to maintain isolation between the electrolyte and the fluid being pumped.
Unlike the preceding patents which all use some form of electric actuation to realize a miniaturized pump, U.S. Pat. No. 5,788,468 deals with a magnetically actuated pump. And while magnetic actuation is a useful means for reducing the operational voltage, this invention has several limitations. For example, the disclosed invention, and more importantly the technique for its manufacture, describes devices whose actuation vectors are parallel to the substrate upon which the devices are fabricated, severely limiting the volume of fluid that may be moved per stroke. Further, since generating large pressures is proportional to the ability to fabricate electromagnetic coils with large Ampere-turns, it is not clear that any of the proposed embodiments could functionally enjoy the benefits of batch fabrication, operate at high electrical power efficiencies, or have extended operational lifetimes.
All of the presently proposed miniaturized pumps suffer from one of the following deficiencies: limited mass flow capabilities (xcexcl/min), difficult and expensive fabrication processes, excessive valve leakage, inefficient and unreliable operation, and very low pressure heads (less than an atmosphere).
Finally, a miniaturized vacuum system is essential to any number of novel miniaturized systems presently under development. For example, many forms of chemical and scientific testing cannot be performed under conditions other than at reduced pressures. Recently there has been a great deal of interest in the fabrication of miniaturized sensing and analysis devices many of which would benefit from a highly portable, compact, low-power, and efficient method for evacuating a fixed volume and/or maintaining pressures reduced below ambient hereafter referred to as a vacuum. An example of such applications is miniaturized mass-spectrometry; e.g., U.S. Pat. No. 6,157,029. Likewise, a large number of electronic devices, such as field emission tips and miniaturized vacuum tubes, require the maintenance of vacuum to operate; e.g., U.S. Pat. No. 5,763,998. Due to fabrication limitations, the sealed vacuum enclosures of the electronic systems often have significant leak rates. The long-term consequence of these leaks is of course degraded performance. Such systems could clearly benefit from an inexpensive, highly compact vacuum system that could be incorporated into the system architecture and periodically refresh the vacuum of the enclosed devices. Several miniaturized vacuum pumps have been proposed; e.g., U.S. Pat. No. 5,871,336. The invention described in U.S. Pat. No. 5,871,336 can only evacuate very small volumes and under very small flows of higher-pressure gas.
There is a need in the art for improved cooling systems, power generation devices, pumping systems, and vacuum systems.
The present invention provides devices and methods for cooling, generating power, pumping fluids/compressing gases, and producing a vacuum. These devices and methods are capable of being miniaturized, use a reciprocating piston, are highly efficient, and are capable of being mass-produced using the broad class of microfabrication techniques mentioned above and informally known as Micro-Electro-Mechanical Systems (MEMS) processes or conventional processes.
In one embodiment, the present invention is a highly compact, modular, low-cost, lightweight, miniaturized heat pump/heat engine. This heat pump/heat engine can be used to produce significant amounts of cooling down to cryogenic temperatures, to generate significant amounts of power, to pump substantial amounts of fluids, to compress gases, and to produce a vacuum.
More specifically, there is provided a fluid expander comprising: a housing defining an enclosed work space and having a working fluid, said housing comprising: a first end forming a first plate of a capacitor; a piston slidably disposed in the housing for reciprocating motion to define a variable volume within said housing, said piston having a first side forming a second plate of a capacitor, said second plate in electrostatic or magnetic connection with said first plate; and a control circuit linked to said piston and said first end which controls the strength of the electrostatic or magnetic force between the plates of the capacitor.
The description above describes a single-stage device. It should be recognized that any of the devices described herein may operate as single-stage (single-acting) devices or double-stage (double-acting) devices. For example, in the expander described above, a double-acting device is formed by adding a second end to the housing. In the double-acting device, the piston is slidably disposed in the housing between the first end and the second end for reciprocating motion to define a variable volume within the housing. In addition to the first side of the piston which forms a first capacitor with the first end, in double-acting devices, the piston has a second side in electrostatic connection with the second end of the housing and forms a second capacitor. Also, the control circuit linked to the piston controls the strength of the electrostatic or magnetic force between the first end and the piston and the second end and the piston.
Also provided are methods of using the devices described herein. One exemplary method of use is a method of expanding a gas, the method comprising: applying a clamping voltage between a piston slidably disposed in a housing and a first end of said housing, wherein said piston moves toward said first end but does not contact said first end; allowing a working fluid (pressurized gas, for example) to enter the space between said first end of said housing and said piston; releasing the clamping voltage between said piston and said first end, whereby said piston moves away from said first end and said working fluid is expanded. The expansions described herein are isentropic (i.e., constant entropy). It is understood that a completely isentropic process is impossible because of various losses described herein and known to the art. When the term xe2x80x9cisentropicxe2x80x9d is used herein, it is to be understood that processes that are physically obtainable are referred to, including those processes where the losses, which cause an isentropic process to move from the ideal, are minimized to the extent possible and practical.
All methods described herein may be single-acting or double acting, where the device configuration is altered as discussed above. In double-acting devices, while the piston is energized with respect to the first end of the housing and an associated change in thermodynamic state is occurring in the first end, the mechanical motion of the second end of the housing is preparing the second end for such action in a complementary way. In a double-acting expander, the method comprises: applying a clamping voltage between a piston slidably disposed in a housing and a first end of the housing, the housing defining an enclosed work space and the housing comprising a first end having at least one inlet and at least one outlet and a second end having at least one inlet and at least one outlet, wherein the piston moves toward the first end but does not contact the first end; allowing a working fluid to enter the space between the first end of said housing and the piston; releasing the clamping voltage between the piston and the first end, wherein the working fluid is isentropically expanded and the piston moves away from the first end and toward the second end; applying a clamping voltage between the piston and the second end of the housing, wherein the piston moves toward the second end but does not contact the second end; allowing a working fluid to enter the space between the second end of the housing and the piston; releasing the clamping voltage between the piston and the second end, wherein the working fluid is isentropically expanded and the piston moves away from the second end and toward the first end. The cycle can be repeated as desired.
As used herein, energizing or activating means a suitable force is applied to a component (piston, for example), or section (capacitor formed between the piston and first end, for example) to produce the desired effect. As described herein, the piston may be energized electrically or magnetically, or using a combination of both methods.
Also provided is a method of generating power comprising: placing a combustible substance in the first end of a housing having a first end and a second end and a piston slidably disposed in said housing for reciprocating motion to define a variable volume within the housing, the piston having a first side in electrostatic or magnetic connection with the first end of said housing and forming a first capacitor and a second side in electrostatic or magnetic connection with the second end of the housing and forming a second capacitor; energizing the piston by applying a force to the piston so that the piston is moved toward the first end; igniting the combustible substance, thereby increasing the temperature and pressure in the first end; reducing the force on the piston allowing the combustible substance to expand against the energized capacitors formed by the piston and the housing, thereby generating power. The power may be harnessed or transferred by any means known in the art.
Also provided is another method of generating power comprising: applying a clamping voltage between the first end of a housing and a piston slidably disposed in the housing and in electrical or magnetic connection with the first end of the housing; admitting heated gas or fluid into the first end of a housing; releasing the clamping voltage on the piston; allowing the piston to expand away from the first end, thereby generating power. This heated gas may be supplied by heat generated from any source including the type of heat generated from electronics or by combustion products.
Also provided is a method of pumping a substance comprising: placing a compressible substance in the first end of a housing having a first end having at least one inlet and at least one outlet, and a second end having at least one inlet and at least one outlet, a piston slidably disposed in the housing between the first end and the second end for reciprocating motion to define a variable volume within the housing, the piston having a first side in electrostatic or magnetic connection with the first end of the housing and forming a first capacitor, the piston having a second side in electrostatic connection with the second end of the housing and forming a second capacitor; energizing the piston by applying a force to the piston so that the piston moves toward the first end, whereby the temperature and pressure of the compressible substance are increased; removing the compressible substance from the first end of the housing. A means for double action is also provided by placing a compressible substance in the second end of the housing, energizing the piston by applying a force to the piston so that the piston moves toward the second end, whereby the temperature and pressure of the compressible substance are increased; removing the compressible substance from the second end of the housing.
Also provided is a method of reducing the pressure in a vessel in gas or fluid connection with a housing comprising: simultaneously minimizing the volume of the first end of a housing having a first end and a second end, separated by a piston slidably disposed in the housing between the first end and the second end for reciprocating motion to define a variable volume within the housing, the piston having a first side in electrostatic or magnetic connection with the first end of the housing and forming a first capacitor and a second side in electrostatic or magnetic connection with the second end of the housing and forming a second capacitor; when the second end has the volume maximized, thereby reducing the pressure in the second volume. Gas at a higher pressure than that present in the second end is then admitted from the vessel into the second end raising the pressure of the second end and incrementally decreasing the pressure of the vessel. The gas in the second end is expelled through an outlet by energizing the piston so that it moves toward the second end reducing the volume of the second end simultaneously increasing the volume of the first end reducing the pressure of the gas in the first end, thereby providing a means for double action when the volume of the second end has been minimized and the volume of the first end has been maximized.
Also provided are ways of using the devices described herein in a cooling system, for example comprising: a cooler in thermal connection with an object to be cooled; a compressor comprising a housing having a first end having at least one inlet and at least one outlet, a second end having at least one inlet and at least one outlet; a piston slidably disposed in the housing between said first end and said second end for reciprocating motion to define a variable volume within said housing, said piston having a first side in electrostatic or magnetic connection with said first end of said housing and forming a first capacitor, said piston having a second side in electrostatic connection with said second end of said housing and forming a second capacitor; and means for providing electrical or magnetic control to said device, said compressor in fluid or gas connection with said cooler; a heat exchanger in fluid or gas connection with said compressor and said cooler, whereby in operation, cooling is provided to the desired level. Also provided is a means whereby the cooler may be an expander, which uses the expansion method, provided herein.
Also provided is a cooling system comprising: a precooler; a compressor in fluid connection with said precooler; a first heat exchanger in fluid connection with said compressor; an expander in fluid or gas connection with said first heat exchanger, said expander comprising a first end having at least one inlet and at least one outlet, a second end having at least one inlet and at least one outlet, a piston slidably disposed in the housing between said first end and said second end for reciprocating motion to define a variable volume within said housing, said piston having a first side in electrostatic or magnetic connection with said first end of said housing and forming a first capacitor, said piston having a second side in electrostatic connection with said second end of said housing and forming a second capacitor; a second heat exchanger in fluid or gas connection with said expander; control electronics which are in electrical connection with said expander and said compressor. Also provided is a means whereby said precooler may be an expander using the method of expansion described herein.
Also provided is a method for mechanical voltage/energy conversion comprising: applying a force between a first end of a housing and a piston in a housing having a first end having at least one inlet and at least one outlet, a second end having at least one inlet and at least one outlet, and a piston slidably disposed in the housing between said first end and said second end for reciprocating motion to define a variable volume within said housing, said piston having a first side in electrostatic or magnetic connection with said first end of said housing and forming a first capacitor, said piston having a second side in electrostatic connection with said second end of said housing and forming a second capacitor; opening said inlet to said first end; inserting gas into said first end through said inlet; reducing the force between said first end and said piston so that said piston is able to move; closing the inlet valve to said first end, whereby the gas in said first end expands, increasing the electrical potential between the first end and the piston.
Also provided is a means whereby electrostatic forces may be used to align the piston to the electrodes. This self-aligned structure can be formed as described herein and known to one of ordinary skill in the art. The invention may be used as a liquefaction system for various gases, as will be evident from the disclosure. The devices may be operated continuously by repeating the steps, as known in the art.
Other uses for the devices described herein are included in the invention and will be readily apparent to one of ordinary skill in the art.